Speed control method

ABSTRACT

A method for controlling an engine having both an electronically controlled inlet device, such as an electronic throttle unit, and an electronically controlled outlet device, such as a variable cam timing system is disclosed. The method of the present invention achieves cylinder air charge control that is faster than possible by using an inlet device alone. In other words, the method of the present invention controls cylinder air charge faster than manifold dynamics by coordination of the inlet and outlet device. This improved control is used to improve various engine control functions.

The present application is a divisional of U.S. patent application Ser.No. 10/798,759, filed on Mar. 11, 2004, now U.S. Pat. No. 6,962,139which is a divisional of U.S. patent application Ser. No. 10/370,025,filed on Feb. 20, 2003, now U.S. Pat. No. 6,945,225 which is adivisional of U.S. patent application Ser. No. 09/420,322, filed on Oct.18, 1999 now U.S. Pat. No. 6,560,527.

FIELD OF THE INVENTION

The field of the invention relates to engine speed control in internalcombustion engines.

BACKGROUND OF THE INVENTION

A vehicle's engine typically utilizes an idle speed control mode whereengine speed is controlled to a desired speed when a vehicle isstationary or slowly moving and an operator is not requesting drivetorque. During idle conditions, it is desirable to maintain a constantengine speed, thereby giving the operator superior drive feel. To keepengine speed constant, idle speed control should reject engine torquedisturbances from various sources, such as, for example, airconditioning systems, power steering systems, changes in ambientconditions, or changes in any other devices that affect engine speed.

One method for control ling engine speed to a desired speed usesignition timing, throttle position, or a combination of both. In onesystem a torque reserve is used so that it is possible to rapidlyincrease engine torque using ignition timing, thereby controlling enginespeed. One example of a system using ignition timing is disclosed inU.S. Pat. No. 5,765,527.

The inventors herein have recognized several disadvantages with theabove approaches. In particular a disadvantage with using throttleposition is that the throttle cannot quickly change engine torque sinceit controls flow entering an intake manifold. Controlling flow enteringthe manifold cannot rapidly control cylinder charge due to manifoldvolume. For example, if the throttle is instantly closed, cylinder aircharge does not instantly decrease to zero. The engine must pump downthe air stored in the manifold, which takes a certain number ofrevolutions. Therefore, the cylinder air charge gradually decreasestoward zero.

Another disadvantage with the known approaches is related to ignitiontiming. In particular, to maximize fuel economy, ignition timing shouldbe at MBT timing (ignition timing for maximum torque). However, when atMBT, adjustment of ignition timing in any direction decreases enginetorque and fuel economy. Therefore, when maximizing fuel economy, loadtorques cannot be rejected since ignition timing can only decreaseengine torque. To be able to use ignition timing in both positive andnegative directions, ignition timing must be set away from MBT timing.This allows rapid engine torque control, but at the cost of degradedfuel economy.

SUMMARY OF THE INVENTION

An object of the present invention is to rapidly control engine speed toa desired engine speed while maximizing fuel economy.

The above object is achieved and disadvantages of prior approachesovercome by a method for controlling speed of an engine having at leastone cylinder, the engine also having an intake manifold and an outletcontrol device for controlling flow from the intake manifold into thecylinder, comprising: generating a desired engine speed; and changingthe outlet control device to control the engine speed to said desiredengine speed.

By using an outlet control device that controls flow exiting themanifold (entering the cylinder), it is possible to rapidly changeengine torque and engine speeds despite response delays of airflowinducted through the intake manifold. In other words, a rapid to changein cylinder charge can be achieved, thereby allowing a rapid change incylinder air/fuel ratio while preventing disturbances in engine torque.

An advantage of the above aspect of the invention is that engine speedcan be more accurately controlled to a desired engine speed without fueleconomy degradation.

In another aspect of the present invention, the above object is achievedand disadvantage of prior approaches overcome by a method forcontrolling speed of an engine having at least one cylinder, the enginealso having an intake manifold and an outlet control device forcontrolling flow from the intake manifold into the cylinder and an inletcontrol device for controlling flow into the intake manifold,comprising: generating a desired engine speed; and changing both theoutlet control device and the inlet control device based on the enginespeed and said desired engine speed and in response to a respectiveoutlet control device command and an inlet control device command.

By changing both the inlet and outlet control devices, it is possible torapidly change engine torque and engine speed despite response delays ofairflow inducted through the intake manifold. Since the cylinder aircharge can be rapidly changed, the cylinder air/fuel ratio change can becompensated and abrupt changes in engine torque can be avoided. In otherwords, the present invention controls manifold inlet and outlet flows ina coordinated way to allow a rapid change in engine speed regardless ofmanifold volume. This rapid cylinder air charge change allows torquedisturbances to by rapidly rejected without using an ignition timingtorque reserve.

An advantage of the above aspect of the invention is that sustainedtorque disturbances can rejected.

Another advantage of the above aspect of the invention is that by usingboth an outlet and an inlet control device, a more controlled rapidchange in engine torque and engine speed.

Other objects, features and advantages of the present invention will bereadily appreciated by the reader of this specification.

BRIEF DESCRIPTION OF THE DRAWINGS

The object and advantages of the invention claimed herein will be morereadily understood by reading an example of an embodiment in which theinvention is used to advantage with reference to the following drawingswherein:

FIGS. 1A and 1B are a block diagrams of an embodiment in which theinvention is used to advantage;

FIG. 2A is a block diagram of an embodiment in which the invention isused to advantage;

FIGS. 2B–2O are graphs describing operation of the embodiment in FIG.2A;

FIGS. 3–5, 8–10 are high level flowcharts which perform a portion ofoperation of the embodiment shown in FIGS. 1A, 1B, and 2A;

FIG. 6 is a graph showing how various factors are related to engineoperation according to the present invention;

FIG. 7 is a graph depicting results using the present invention;

FIGS. 11A–11F are graphs describing operation to of an embodiment of thepresent invention; and

FIGS. 12 and 14 are a block diagrams of an embodiment in which theinvention is used to advantage.

DESCRIPTION OF PREFERRED EMBODIMENT(S)

Direct injection spark ignited internal combustion engine 10, comprisinga plurality of combustion chambers, is controlled by electronic enginecontroller 12. Combustion chamber 30 of engine 10 is shown in FIG. 1Aincluding combustion chamber walls 32 with piston 36 positioned thereinand connected to crankshaft 40. In this particular example, piston 30includes a recess or bowl (not shown) to help in forming stratifiedcharges of air and fuel. Combustion chamber, or cylinder, 30 is showncommunicating with intake manifold 44 and exhaust manifold 48 viarespective intake valves 52 a and 52 b (not shown), and exhaust valves54 a and 54 b (not shown). Fuel injector 66A is shown directly coupledto combustion chamber 30 for delivering liquid fuel directly therein inproportion to the pulse width of signal fpw received from controller 12via conventional electronic driver 68. Fuel is delivered to fuelinjector 66A by a conventional high pressure fuel system (not shown)including a fuel tank, fuel pumps, and a fuel rail.

Intake manifold 44 is shown communicating with throttle body 58 viathrottle plate 62. In this particular example, throttle plate 62 iscoupled to electric motor 94 so that the position of throttle plate 62is controlled by controller 12 via electric motor 94. This configurationis commonly referred to as electronic throttle control (ETC) which isalso utilized during idle speed control. In an alternative embodiment(not shown), which is well known to those skilled in the art, a bypassair passageway is arranged in parallel with throttle plate 62 to controlInducted airflow during idle speed control via a throttle control valvepositioned within the air passageway.

Exhaust gas oxygen sensor 76 is shown coupled to exhaust manifold 48upstream of catalytic converter 70. In this particular example, sensor76 provides signal EGO to controller 12 which converts signal EGO intotwo-state signal EGOS. A high voltage state of signal EGOS indicatesexhaust gases are rich of stoichiometry and a low voltage state ofsignal EGOS indicates exhaust gases are lean of stoichiometry. SignalEGOS is used to advantage during feedback air/fuel control in aconventional manner to maintain average air/fuel at ₅toichiometry duringthe stoichiometric homogeneous mode of operation.

Conventional distributorless ignition system 88 provides ignition sparkto combustion chamber 30 via spark plug 92 in response to spark advancesignal SA from controller 12.

Controller 12 causes combustion chamber 30 to operate in either ahomogeneous air/fuel mode or a stratified air/fuel mode by controllinginjection timing. In the stratified mode, controller 12 activates fuelinjector 66A during the engine compression stroke se that fuel issprayed directly into the bowl of piston 36. Stratified air/fuel layersare thereby formed. The strata closest to the spark plug contains astoichiometric mixture or a mixture slightly rich of stoichiometry, andsubsequent strata contain progressively leaner mixtures. During thehomogeneous mode, controller 12 activates fuel injector 66A during theintake stroke so that a substantially homogeneous air/fuel mixture isformed when ignition power is supplied to spark plug 92 by ignitionsystem 88. Controller 12 controls the amount of fuel delivered by fuelinjector 66A so that the homogeneous air/fuel mixture in chamber 30 canbe selected to be at stoichiometry, a value rich of stoichiometry, or avalue lean of stoichiometry. The stratified air/fuel mixture will alwaysbe at a value lean of stoichiometry, the exact air/fuel being a functionof the amount of fuel delivered to combustion chamber 30. An additionalsplit mode of operation wherein additional fuel is injected during theexhaust stroke while operating in the stratified mode is also possible.

Nitrogen oxide (NOx) absorbent or trap 72 is shown positioned downstreamof catalytic converter 70. NOx trap 72 absorbs NOx when engine 10 isoperating lean of stoichiotmetry. The absorbed NOx is subsequentlyreacted with HC and catalyzed during a NOx purge cycle when controller12 causes engine 10 to operate in either a rich homogeneous mode or astoichiometric homogeneous mode.

Controller 12 is shown in FIG. 1A as a conventional microcomputerincluding: microprocessor unit 102, input/output ports 404, anelectronic storage medium for executable programs and calibration valuesshown as read only memory chip 106 in this particular example, randomaccess memory 108, keep alive memory 110, and a conventional data bus.Controller 12 is shown receiving various signals from sensors coupled toengine 10, in addition to those signals previously discussed, including:measurement of inducted mass air flow (MAP) from mass air flow sensor100 coupled to throttle body 58; engine coolant temperature (ECT) fromtemperature sensor 112 coupled to cooling sleeve 114; a profile ignitionpickup signal (PIP) from Hall effect sensor 118 is coupled to crankshaft40; and throttle position TP from throttle position sensor 120; andabsolute Manifold Pressure signal MAP from sensor 122. Engine speedsignal RPM is generated by controller 12 from signal PIP in aconventional manner and manifold pressure signal MAP provides anindication of engine load. In a preferred aspect of the presentinvention, sensor 118, which is also used as an engine speed sensor,produces a predetermined number of equally spaced pulses everyrevolution of the crankshaft.

In this particular example, temperature Tcat of catalytic converter 70and temperature Ttrp of NOx trap 72 are interred from engine operationas disclosed in U.S. Pat. No. 5,414,994, the specification of which isincorporated herein by reference. In an alternate embodiment,temperature Tcat is provided by temperature sensor 124 and temperatureTtrp is provided by temperature sensor 126.

Continuing with FIG. 1A, camshaft 130 of engine 10 is showncommunicating with rocker arms 132 and 134 for actuating intake valves52 a, 52 b and exhaust valve 54 a. 54 b. Camshaft 130 is directlycoupled to housing 136. Housing 136 forms a toothed wheel having aplurality of teeth 138. Housing 136 is hydraulically coupled to an innershaft (not shown), which is in turn directly linked to camshaft 130 viaa timing chain (not shown). Therefore, housing 136 and camshaft 130rotate at a speed substantially equivalent to the inner camshaft. Theinner camshaft rotates at a constant speed ratio to crankshaft 40.However, by manipulation of the hydraulic coupling as will be describedlater herein, the relative position of camshaft 130 to crankshaft 40 canbe varied by hydraulic pressures in advance chamber 142 and retardchamber 144. By allowing high pressure hydraulic fluid to enter advancechamber 142, the relative relationship between camshaft 130 andcrankshaft 40 is advanced. Thus, intake valves 52 a, 52 b and exhaustvalves 54 a, 54 b open and close at a time earlier than normal relativeto crankshaft 40. Similarly, by allowing high pressure hydraulic fluidto enter retard chamber 144, the relative relationship between camshaft130 and crankshaft 40 is retarded. Thus, intake valves 52 a, 52 b andexhaust valves 54 a, 54 b open and close at a time later than normalrelative to crankshaft 40.

Teeth 138, being coupled to housing 136 and camshaft 130, allow formeasurement of relative cam position via cam timing sensor 150 providingsignal VCT to controller 12. Teeth 1, 2, 3, and 4 are preferably usedfor measurement of cam timing and are equally spaced (for example, in aV-8 dual bank engine, spaced 90 degrees apart from one another), whiletooth 5 is preferably used for cylinder identification, as describedlater herein. In addition, controller 12 sends control signals(LACT,RA.CT) to conventional solenoid valves (not shown) to control theflow of hydraulic fluid either into advance chamber 142, retard chamber144, or neither.

Relative cam timing is measured using the method described in U.S. Pat.No. 5,548,995, which is incorporated herein by reference. In generalterms, the time, or rotation angle between the rising edge of the PIPsignal and receiving a signal from one of the plurality of teeth 138 onhousing 136 gives a measure of the relative cam timing. For theparticular example of a V-8 engine, with two cylinder banks and a fivetoothed wheel, a measure of cam timing for a particular bank is receivedfour times per revolution, with the extra signal used for cylinderidentification.

Referring now to FIG. 1B, a port fuel injection configuration is shownwhere fuel injector 66B 20 is coupled to intake manifold 44, rather thandirectly cylinder 30.

Referring now to FIG. 2A, a more general diagram shows manifold 44 a,with inlet flow, m_in, and outlet flow, m_out. Inlet flow, m_in, isgoverned by inlet control device 170. Outlet flow, m_out, is governed byoutlet flow device 171. In a preferred embodiment, manifold 44 a is anintake manifold of an engine, inlet control device 170 is a throttle,and outlet control device 171 is a variable cam timing mechanism.However, as one skilled in the art would recognize, there are manyalternative embodiments of the present invention. For example, outletcontrol device could be a swirl control valve, a variable valve timingmechanism, a variable valve lift mechanism, or an electronicallycontrolled intake valve used in camless engine technology.

Continuing with FIG. 2A, there are other 5 variables that affect flowentering and exiting manifold 44 a. For example, pressures p1 and p2,along with inlet control device 170, determine flow m_in. Similarly,pressures p2 and p3, along with outlet device 171 determine flow m_out.Therefore, flow storage in manifold 44 a, which dictates how fastpressure p2 can change, affects flow m_out. In an example where manifold44 a is an intake manifold of an engine operating at stoichiometry, flowm_out represents flow entering a cylinder and is directly proportionalto engine torque.

FIGS. 2B–2K illustrates the effect of such interrelationships on systemperformance. In FIG. 2B, inlet control device 170 is rapidly changed attime t1. The resulting change in outlet flow (m_out) is shown in FIG.2C. The resulting change in inlet flow (m_in) is shown in FIG. 2D. Thisexample has outlet control device 171 fixed, and therefore representsconventional engine operation and prior art operation where throttleposition is used to control outlet flow (m_out). In this example, arapid change in inlet control device 170 does not produce an equallyrapid change in exit flow m_out. According to the present invention, inFIG. 2E, outlet control device, 171 is rapidly changed at time t2. Theresulting change in outlet flow (m_out) is shown in FIG. 2F. Theresulting change in inlet flow (m_in) is shown in FIG. 2G. This examplehas inlet control device 170 fixed, and therefore represents adjustmentof outlet device 170 only to control outlet flow (m_out) In thisexample, a rapid change in outlet control device 170 does produce anequally rapid change in exit flow m_out. However, the rapid change isnot completely sustained.

According to the present invention, in FIG. 2H, inlet control device 170is rapidly changed at time t3. Similarly, in FIG. 2I, outlet controldevice 171 is rapidly changed at time t3. The resulting change in outletflow (m_out) is shown in FIG. 2J. The resulting change in inlet flow(m_in) is shown in FIG. 2K. This example varies both inlet controldevice 170 and outlet control device 170 concurrently. In this example,a rapid change in both inlet control device and 170 outlet controldevice 171 does produce an equally rapid change in exit flow m_out,where the rapid change is sustained.

According to the present invention, in FIG. 2L, inlet control device 170is rapidly changed at time t4. Similarly, in FIG. 2N, outlet controldevice 171 is rapidly changed at time t4 to a greater extent than inFIG. 2I. The resulting change in outlet flow (m_out) is shown in FIG.2N. The resulting change in inlet flow (m_in) is shown in FIG. 2O. Thisexample varies both inlet control device 170 and outlet control device170 concurrently. In this example, a rapid change in both Inlet controldevice and 170 outlet control device 171 does produce an equally rapidchange in exit flow m_out, where the rapid change is sustained andactually produces a certain amount of peak, or overshoot. Thisrepresents how the present invention can be used to not only rapidlyproduce an increase in outlet flow, but to also add an overshoot. Thus,a control system according to the present invention can thereforegenerate an airflow lead control. Such lead control is advantageous forengine idle speed control to counteract engine inertia, or for vehiclelaunch conditions, to give improved drive feel.

According to the present invention, by using an outlet control device itis possible to rapidly control flow exiting a manifold. Further, bycontrolling both an inlet and outlet control device it is possible tomore accurately rapidly control flow exiting a manifold in variousshapes.

In cases where engine 10 operates at a stoichiometric air/fuel ratio,then engine torque directly proportional to cylinder charge, which is inturn proportional to exit flow m_out and engine speed. Thus, accordingto the present invention, by controlling engine airflow to a desiredvalue.

Engine Idle Speed Control

Referring now to FIG. 3, a routine is described for controlling enginespeed using both throttle position and cam timing. In step 310, anengine speed error (Nerr) is calculated based on a difference betweenthe desired engine speed (Ndes) and an actual engine speed (Nact). Then,in step 320, the desired change in cylinder charge is calculated fromspeed error using controller K1, where controller K1 is represented inthe Laplace domain as K1(s) as is known to those skilled in the art. Thedesired in cylinder charge (Amcyl) is preferably calculated using aproportional controller. Therefore, in the preferred embodiment,controller K1 represents a proportional controller. However, as thoseskilled in the art will recognize, various other control schemes can beused in place of proportional controller K1. For example, proportionalintegral derivative controllers, or sliding mode controllers, or anyother controllers known to those skilled in the art, can be used. Next,in step 330, an intermediate throttle position (Tpint) is calculatedfrom speed error and controller K3. As described above, variouscontrollers can be used for controller K3. In a preferred embodiment,controller K3 is an integral controller. Next, in step 340, a nominalcam timing error (VCTerr) is calculated based on a difference between adesired nominal cam timing (VCTdesnom) and an actual cam timing(VCTact). Desired nominal cam timing (VCTdesnom) can be determined basedon operating conditions, for example, based on idle mode, or drive mode.Also, desired nominal cam timing (VCTdesnom) can be set as a function ofdesired engine torque, or any other steady state scheduling method knownto those skilled in the art. Next, in step 350, an intermediate timing(VCTint) is calculated from nominal cam timing error and controller K2.Controller K2 can be any controller known to those skilled in the art.In the preferred embodiment, controller K2 is a proportional integralcontroller.

Referring now to FIG. 4, a routine is described for calculatingadjustments to cam timing and throttle position to rapidly changecylinder charge. First, in step 410, manifold pressure (Pm) is estimatedor measured using sensor 122. In the preferred embodiment, manifoldpressure (Pin) is estimated using methods known to those skilled in theart. For example, manifold pressure can be estimated using signal MAFfrom mass airflow sensor 100, engine speed, and other signals known tothose skilled in the art to effect manifold pressure. Next, in step 412,the desired change in cylinder charge (Δncyl) is read from FIG. 3. Next,in step 414, a change in cam timing (ΔVCT) is determined to give thedesired change in cylinder charge at manifold pressure (Pm) read in step410. Step 414 is performed using maps relating to cam timing, cylindercharge, and manifold pressure. The maps can be determined theoreticallyusing engine models or measured using engine test data. Next, in step416, a change in throttle position (ΔTP) is determined to give thedesired change in cylinder charge (Δncyl) at manifold pressure (Pm)determined in step 410. Step 416 is similarly performed usingcharacteristic maps relating parameters, throttle position, cylindercharge, and manifold pressure. The maps can be determined either usingengine models or engine test data.

Regarding FIG. 5, the routine is described for calculating the desiredcam timing and desired throttle position. First, in step 510, a desiredcylinder, desired cam timing (VCTdes) is determined based on the desiredchange in cam timing and intermediate cam timing. Next, in step 512, thedesired throttle position (TPdes) is determined based on intermediatethrottle position and desired change in throttle position.

However, when a cam timing position is desired that is greater than amaximum possible cam timing, or when a minimum cam timing is less than aminimum possible cam timing, desired cam timing (VCTdes) is clipped tothe maximum or minimum value. In other words adjustment of cam timingmay not be able to provide the desired increase, or decrease in cylinderair charge. In this case, cam timing is clipped to the achievable limitvalue and throttle position is relied upon to provide control.

Steady State Constraints

As described above herein with particular reference to FIGS. 3–5, acontrol method for controlling engine airflow, or engine torque, andthereby engine speed was described. In addition, the method included amethod for rapidly controlling cylinder charge using both an inlet andoutlet control device, while also relatively slowly controlling theoutlet control device to a nominal position. Both of these processes arenow further illustrated using both FIGS. 6 and 7.

Referring now to FIG. 6, a graph is shown with throttle position (TP) onthe vertical axis and cam timing (VCT) on the horizontal axis. Dashdotted lines are shown for constant values of engine torque (Te),assuming stoichiometric conditions, while solid lines show constantvalue of manifold pressure. According to the present invention, theengine can quickly change operating points along the lines of constantpressure (thereby rapidly changing engine airflow and torque) sincethere are no manifold dynamics in this direction. However, the enginecan change only relatively slowly along the dash dotted lines ifair/fuel ratio is fixed (for example at stoichiometry). The dashedvertical line represents the nominal desired cam timing for the givenoperating conditions. For example, the nominal timing for idleconditions, or the nominal timing for the current desired engine torque.

In other words, manifold dynamics represent dynamics associated withchanging manifold pressure and explain why flow entering the cylinder isnot always equal to flow entering the manifold. Manifold pressure cannotinstantly change due to manifold volume. As manifold volume increases,manifold dynamics become slower. Conversely, as manifold volumedecreases, manifold dynamics become faster. Thus, manifold dynamics, ormanifold delay, is a function of manifold volume. As described above,when moving along lines of constant pressure manifold dynamics areessentially immaterial Therefore flow changes are not limited bymanifold dynamics when inlet and outlet control devices are changed toaffect flow in similar directions. By changing inlet and outlet controldevices faster than manifold dynamics to increase along both theabscissa and ordinate of FIG. 6, cylinder flow changes faster thanmanifold dynamics. Stated another way, cylinder flow changes faster thanit would if only the inlet control device changed infinitely fast. Wheninlet and outlet control devices are changed to affect flow in oppositedirections, cylinder charge can be kept constant. In particular, boththe inlet and outlet control devices are changed slower than manifolddynamics since manifold pressure is changed. This is particularly usefulwhen engine airflow, or engine torque, is to be kept relatively constantyet it is desired to place either the inlet control device or the outletcontrol device in a specified location.

Referring now to both FIGS. 6 and 7, an example of operation accordingto an aspect of the present invention is now described. First, thesystem is operating at point 1. For example, the desired engine torque(Ted) is Te2, or this happens to be the engine torque to maintain adesired engine speed. Then, either the desired engine torque (Ted)changes to Te3, or a torque disturbance causes an engine speed to drop,thereby requiring an increase in engine torque to Te3 to maintain thedesired engine speed. At this point (time t5), controller 12 causes boththe throttle position and cam timing to change so that the engine systemquickly moves to Point 2. Next, in order to maintain cam timing and thenominal cam timing, controller 12 causes both the throttle position andcam timing to move to point 3 at a rate slower than the manifolddynamics.

Thus, according to the present invention, throttle position and camtiming are caused to move in the following way. When it is desired torapidly increase cylinder air charge irrespective of manifold volume: 1)throttle position moves in a way that causes an increase in throttleopening area, and 2) cam timing is adjusted in a way to increase theinducted cylinder air charge for a given manifold pressure is moved.Similarly, when it is desired to rapidly decrease cylinder air chargeirrespective of manifold volume: 1) throttle position moves in a waythat causes a decrease in throttle opening area, and 2) cam timing isadjusted in a way to decrease the inducted cylinder air charge for agiven manifold pressure. Thus, it is possible to rapidly change andmaintain flow into the cylinder by this combined action.

However, when it is desired to maintain cylinder air charge and eitherincrease throttle opening or cause cam timing to move so that less aircharge is inducted for a given manifold pressure, or both, 1) throttleposition moves in a way that causes an increase in throttle openingarea, and 2) cam timing is adjusted in a way to decrease the inductedcylinder air charge for a given manifold pressure. Thus, cylinder chargecan be kept constant by this opposing action. Alternatively, when it isdesired to maintain cylinder air charge and either decrease throttleopening or cause cam timing to move so that more air charge is inductedfor a given manifold pressure, or both, 1) throttle position moves in away that causes a decrease in throttle opening area, and 2) cam timingis adjusted in a way to increase the inducted cylinder air charge for agiven manifold pressure. Again, cylinder charge can be kept constant bythis opposing action.

Such coordinated control is advantageous in that steady stateoptimization constraints on cam timing can be provided while stillproviding the ability to control cylinder air charge rapidly.

Engine Torque Control

Referring now to FIG. 8, a routine is described for controlling enginetorque rather than engine speed as described in FIG. 3. Engine torquecontrol according to the present invention may be used for variousreasons, including normal driving operating, traction control, and/orcruise control. In other words, FIG. 8, along with FIGS. 3–5 can be usedto control engine torque, where steps 310–330 are replaced by FIG. 8.Regarding FIG. 8, first, in step 810, a desired engine torque (Ted) isdetermined. Those skilled in the art will recognize that desired enginetorque (Ted) can be determined in various ways. For example, desiredengine torque (Ted) can be determine from desired wheel torque and gearratio, from pedal position and vehicle speed, from pedal position andengine speed, or any other method known to those skilled in the art.Then, in step 820, desired cylinder charge (mcyld) is determined basedon a function (h) of desired engine torque (Ted). Function (h) is basedon a desired air/fuel ratio, such as stoichiometric conditions.

Continuing with FIG. 8, in step 830, desired change in cylinder charge(Dmcyl) is determined based on the difference between desired cylindercharge (mcyld) and actual cylinder charge (mcyl). Then, in step 840,intermediate throttle position (Tpint) is calculated from desired changein cylinder charge (Dmcyl) and controller K3. As described above,various controllers can be used for controller K3. In a preferredembodiment, controller K3 is an integral controller. Then, in step 850,a nominal cam timing (VCTdesnom) if determined based on function (g) anddesired engine torque (Ted). Then, the routine continues to step 340 inFIG. 3.

Alternative Embodiment for Cylinder Charge, Torque, and Engine SpeedControl

An alternative embodiment is now described that can be used to controleither cylinder air charge, engine torque at a given air/fuel ratio, orengine speed. Referring now to FIG. 9, in step 910, a determination ismade as to whether the engine is currently in an idle condition. Thoseskilled in the art will recognize various methods for determining idleconditions such as accelerator pedal position, engine speed, and variousother factors. When the answer to step 910 is YES, the routine continuesto step 912. In step 912, the desired cylinder charge (mcyldes) based onan engine speed error (Nerr). The desired cylinder charge is calculatedusing function Li, which can represent any function such as, forexample, engine speed error multiplied by a constant gain, which is thepreferred embodiment. Otherwise, when the answer to step 910 is NO, theroutine continues to step 914. In step 914, the desired cylinder chargeis calculated based on either a driver command or operating conditionsusing function (L2). Those skilled in the art will recognize variousmethods for calculating a desired cylinder charge from a driver commandsuch as, for example, to provide a desired engine torque, a desiredwheel torque, an engine output, or provide any other condition requestedby the driver. Those skilled in the art will also recognize variousoperating conditions that can affect a desired cylinder charge such as,for example, engine starting conditions, cold conditions, or crankingconditions.

Continuing with FIG. 9, the routine continues from either step 912 orstep 914 to step 916. In step 916, a cylinder charge error (mcylerr) iscalculated based on desired cylinder charge and actual cylinder charge(mcylact). Next, in step 918, cam timing nominal error is calculated.Next, in step 920, intermediate cam timing is calculated from cam timingnominal error and controller H1. In a preferred embodiment, controllerH1 is an integral controller known to those skilled in the art. Also, ina preferred embodiment, the gains of controller H1 are determined sothat the cam timing is adjusted slower than manifold dynamics. In otherwords, the gains of controller H1 are determined based on manifoldvolume, and engine speed. However, controller H1 can be any controllerknown to those skilled in the art such as, for example, a PIDcontroller, a PI controller, or a P controller. Next, in step 930,intermediate throttle position is calculated from cylinder charge errorand controller H2. In a preferred embodiment, controller H2 is anintegral controller; however, as those skilled in the art willrecognize, various controllers can be used. Next, in step 940, adifference in cam timing is calculated from cylinder charge error andcontroller H3. In a preferred embodiment, controller H3 is a leadcontroller or a high pass filter type controller. Next, the routinecontinues to step 950, where a difference in throttle position iscalculated from the difference in cam timing using controller H4. In apreferred embodiment, controller H4 is simply a constant gain. Next, theroutine continues to FIG. 5.

Air/Fuel Constraints in Lean Conditions

Referring now to FIG. 10, a routine for restricting air/fuel ratio tospecific regions is described. In step 1010, a determination is made asto whether the engine is operating in stratified conditions. When theanswer to step 1010 is YES, the routine continues to step 1012. In step1012, the required fuel injection amount (fi) is calculated based ondriver commands or operating conditions. Again, those skilled in the artwill recognize various methods for determining a fuel injection amountbased on driver command or engine operating conditions. Next, theroutine continues to step 1014, where a restricted air range iscalculated. The restricted air range is calculated using a maximum andminimum allowable air/fuel ratio, the fuel injection amount, and a bandparameter (B). The band parameter is used to allow room for calculationinaccuracies. Next, the routine continues to step 1016, where adetermination is made as to whether actual cylinder charge is betweenthe maximum and minimum allowable cylinder charges (mcy11, mcy12). Whenthe answer to step 1016 is YES, a determination is then made in step1018 as to whether it is possible, given the current operatingconditions, to produce air charge (mcy11). This determination can bemade based on factors such as, for example, engine speed and atmosphericpressure. In particular, as atmospheric pressure increases, engine 10 isable to pump a greater maximum air amount. Therefore, in a preferredembodiment, limit mcyl 11 is selected when atmospheric pressure isgreater than a calibrated value, and mcy12 is selected otherwise. Inother words, in step 1018, a determination is made as to whether theengine can physically produce upper air charge (mcyl 11). When theanswer to step 1018 is NO, the routine sets the desired cylinder charge(mcyldes) equal to lower air charge (mcy12) in step 1020. Otherwise, thedesired cylinder charge is set to upper cylinder charge (mcyl 11).

Referring now to FIG. 11, the present invention is compared to prior artapproaches in controlling engine torque or keeping an air/fuel ratiooutside of a restricted air/fuel ratio range. The FIGS. 11 a through 11f show a comparison of the present invention as represented by solidlines, and prior approaches as represented by dashed lines. In priorapproaches, as shown in FIG. 11 a, fuel injection amount increases attime T6 in response to a change in desired engine torque shown in FIG. 1d. To maintain the air/fuel ratio at a desired point, as shown in FIG.11 e, increased airflow is required. To provide increased airflow, priorapproaches change throttle position, as shown in FIG. 11 c, at time T6.However, because of airflow dynamics due to the manifold volume, aircharge does not increase fast enough, as shown in FIG. 11 f. Thisresults in a temporary excursion in the air/fuel ratio into therestricted region as shown in FIG. 11 e. Thus, the prior approachescannot keep the air/fuel ratio completely out of the restricted region.

According to the present invention, and as described in FIG. 10, at timeT6, cam timing, as shown in FIG. 11 b, is also increased. This allowsthe air/fuel ratio, as shown in FIG. 11 e, to refrain from entering therestricted air/fuel range. This is possible since the airflow wasquickly changed using both cam timing and throttle position as shown inFIG. 11 f by the solid line.

Vehicle Launch Improvement

Vehicle driveability is improved according to the present invention byproviding engine torque increases at a rate faster than available byprior art methods. Regarding FIG. 12, engine is coupled to automatictransmission (AT) 1200 via torque converter (TC) 1210. Automatictransmission (AT) 1200 is shown coupled to drive shaft 1202, which inturn is coupled to final drive unit (FD) 1204. Final drive unit (FD) iscoupled wheel 1208 via second drive shaft 1208. In this configuration,engine 10 can be somewhat downsized and still produce acceptable drivefeel by controlling engine torque or airflow using both throttleposition and cam timing as describe above herein.

Regarding FIG. 13, torque converter 1210 is removed. Thus, even withoutdownsizing engine 10, using prior approaches driveability is reduced. Inother words, vehicle launch is normally assisting from torquemultiplication provided by torque converter 1210. Without torqueconverter 1210, vehicle launch feel is degraded. To compensate for thelack of torque converter 1210, engine 10 is controlled according to thepresent invention using both throttle position and cam timing to rapidlyincrease engine torque or airflow, thereby improving drive feel andallowing elimination of torque converter 1210.

In a preferred embodiment, during vehicle launch at low vehicle speedand low engine speed, both inlet control device and outlet controldevice 170 and 171 are coordinated to rapidly control engine cylindercharge, thereby improving drive feel. Further to enable such operating,nominal cam timing (VCTdesnom) is set to a value where a large potentialincrease in cylinder air 10 charge can be achieved when the transmissionis in drive and vehicle speed is below a predetermine vehicle speedindicating potential for vehicle launch.

Turbo Lag Compensation

Referring now to FIG. 14, a configuration is shown where engine 10 iscoupled to a compression device 1400. In a preferred embodiment,compression device 1400 is a turbocharger. However, compression device1400 can be any compression device such as, for example, a supercharger.Engine 10 is shown coupled to intake manifold 44 b and exhaust manifold48 b. Also shown is outlet control device 171 coupled between intakemanifold 44 b and engine 10. Inlet control device 170 is also showncoupled between intake manifold 44 b and compression device 1400.Compression device 1400 contains compressor 1410.

According to the present invention, it is now possible to compensate fordelays related to turbo lag. In a preferred embodiment, during vehiclelaunch at low vehicle speed and low engine speed, both inlet controldevice and outlet control device 170 and 171 are coordinated to rapidlycontrol engine cylinder charge, thereby compensating for the delayedpressure buildup from compression device 1400. However, such an approachcan be used throughout various driving conditions, such as, for example,during highway cruising operation.

While the invention has been shown and described in its preferredembodiments, it will be clear to those skilled in the art, to which itpertains, that many changes and modifications may be made theretowithout departing from the scope of the invention. For example, asdescribed above herein, any device that affects flow exiting intakemanifold 44 and entering cylinder 30 can be used as an outlet controldevice. For example, a swirl control valve, a charge motion controlvalve, an intake manifold runner control valve, or an electronicallycontrolled intake valve can be used according to the present inventionto rapidly change cylinder fresh charge. Further, any device thataffects flow entering intake manifold 44 can be used in place of intakecontrol device. For example, an EGR valve, a purge control valve, or anintake air bypass valve can be used in conjunction with the outletcontrol device so rapidly change cylinder fresh charge.

Also, the invention can be applied to any situation where enginecylinder charge needs to be controlled faster than manifold dynamicswould normally allow. Accordingly, it is intended that the invention belimited only by the following claims.

1. A method for controlling an engine airflow, the engine having atleast one cylinder, the engine also having an intake manifold and anoutlet control device for controlling flow from the intake manifold intothe cylinder, the outlet control device including variable valve lift,the engine having an exhaust system with a three-way catalytic converterand exhaust gas oxygen sensor, the method comprising: generating adesired engine speed; changing valve lift to control the engine speed tosaid desired engine speed; directly injecting fuel into the cylinderbased on a signal from the sensor to maintain average air/fuel atstoichiometry.
 2. The method of claim 1 wherein the sensor is locatedupstream of the three-way catalyst.
 3. The method of claim 1 wherein theengine also has an electronic throttle coupled to said intake manifold,the method further comprising adjusting said throttle based on anoperating condition.
 4. The method of claim 1 wherein said adjustingfurther comprises adjusting valve lift based on an error between saidengine speed and determined engine speed.
 5. The method of claim 1wherein the engine is a v-type dual bank engine.
 6. The method of claim1 wherein said directly injecting fuel further comprises directlyinjecting fuel into the cylinder during the intake stroke so that asubstantially homogeneous air/fuel mixture is formed.